From the viewpoint of high production efficiency, reduction in cost of curing energy, and VOC reduction, active energy ray-curing systems have been widely used. In particular, an ultraviolet curing system becomes a main stream because of its lower introduction cost and smaller installation area of equipment than other active energy ray curing systems. In the ultraviolet curing system, a photoinitiator is an essential component for starting curing, but the photoinitiator or a decomposition product thereof remains as a low-molecular-weight component in a coating film after curing because the photoinitiator is generally a low-molecular-weight compound. Such a low-molecular-weight component causes an odor of a coating film and an eluted material from the coating film. In particular, in application to ultraviolet curable inks used for printed matters for food packaging, it is strongly demanded to improve migration in which the remaining photoinitiator eluted from a cured product migrates to the back side of a printed matter in direct contact with a food.
For example, Patent Literature 1 discloses an oligomer-type photoinitiator having a plurality of initiator groups in its molecule. A method disclosed in this literature has the effect of decreasing an odor and migration by oligomerizing a photoinitiator, but migration cannot be completely suppressed.
In addition, Patent Literatures 2 and 3 each disclose an ultraviolet ray-durable resin produced by Michael addition reaction between a polyfunctional acrylate and a photoinitiator containing a β-dicarbonyl group. A method disclosed in these literatures is capable of significantly decreasing elusion of a photoinitiator from a cured film by introducing a reactive group in a photoinitiator group and immobilizing the photoinitiator group in the cured film. However, the method exhibits insufficient curing performance and thus has the problem of causing defective curing in application in which a curing rate is required, particularly application to ultraviolet ray-curable inks.